The present invention relates to projection optical systems and exposure apparatus incorporating same and methods pertaining to same, and in particular to such systems, apparatus and methods for manufacturing devices and elements, such as integrated circuits, liquid crystal displays, detectors, MR (magneto-resistive) heads, and the like.
Step-and-repeat and step-and-scan projection exposure apparatus are presently used to manufacture semiconductor devices and the like. In step and repeat projection exposure apparatus (xe2x80x9csteppersxe2x80x9d), each exposure field is exposed in a single static exposure. In step-and-scan projection exposure apparatus (xe2x80x9cscannersxe2x80x9d), each exposure field is scanned during exposure. A projection exposure apparatus as used in semiconductor manufacturing, for example, transfers an image of a pattern on a reticle, which is used as a mask, through a projection optical system and onto a wafer (or glass plate or like workpiece) coated with a photo-sensitive medium, such as photoresist. With the increasing miniaturization of the patterns of semiconductor integrated circuits and other similar devices, there is an increasing demand to increase the resolving power of projection optical systems incorporated into projection exposure apparatus. The resolving power of the projection optical system can be increased by either shortening the exposure wavelength or increasing the image-side numerical aperture (NA).
The wavelengths used in projection exposure apparatus for semiconductor manufacturing are principally mercury lamp g-line (xcex=436 nm) to the i-line (xcex=365 nm). More recently, efforts are being made to employ shorter wavelength light sources, for example excimer lasers (xcex=248 nm, 193 nm). Consequently, projection optical systems are being developed that have optical characteristics that can be used with exposure light of short wavelength. In addition, the demand for both increased resolving power and reduced image distortion in projection optical systems has increased. Image distortion as a whole includes several contributing factors, such as distortion inherent in the projection optical system, distortion due to warping of the wafer upon which the circuit pattern is printed, and distortion due to warping of the reticle on which the circuit pattern to be imaged resides.
To reduce the effect of image distortion due to warping of the wafer, imagewise telecentric projection optical systems have been developed. In such systems, the exit pupil is located at infinity objectwise of the projection optical system. Likewise, to reduce image distortion due to warpage of the reticle, objectwise telecentric optical systems have been employed, wherein the entrance pupil of the projection optical system is located at infinity imagewise of the projection optical system. Such projection optical systems are disclosed in, for example, Japanese Patent Application Kokai No. Sho 63-118115, U.S. Pat. No. 5,260,832 and Japanese Patent Application Kokai No. Hei 5-173065.
In addition, there have been demands for being able to select and adjust the NA to be more ideally suited for printing particular types of patterns on the reticle, as well as to account for other manufacturing conditions. In particular, there have been demands for the projection optical systems in exposure apparatus to have a variable aperture stop whose size can be varied to change the NA of the projection optical system.
Also, if a plurality of lens surfaces in the projection optical system are made aspherical, it is possible to reduce the number of lenses used. Examples of such projection optical systems are disclosed in, for example, U.S. Pat. No. 4,928,238, Japanese Patent Application Kokai No. Hei 5-34593 and Japanese Patent Application Kokai No. Hei 7-128592.
As described above, it is desirable to make the projection optical system both imagewise and objectwise telecentric (i.e., xe2x80x9cdouble-telecentricxe2x80x9d) to reduce the effects of both wafer warping and reticle warping on image distortion. Therefore, as disclosed in the abovementioned patent applications, projection optical systems have been developed that are double-telecentric. Nevertheless, in prior art double-telecentric projection optical systems, it has proven difficult to make the NA sufficiently large while simultaneously reducing the various aberrations over a large exposure field. In particular, in the prior art systems, distortion correction is generally inadequate.
Moreover, in the prior art projection optical systems, if a variable aperture stop is provided to vary the NA of the projection optical system, vignetting occurs at the periphery of the exposure field due to spherical aberration at the pupil when the aperture stop size is changed. Consequently, uniformity of illumination suffers in the exposure field periphery. In addition, telecentricity degrades when the numerical aperture is varied, and there is also the problem that the exposure field size cannot be increased.
Furthermore, the projection optical systems with aspherical surfaces disclosed in the abovementioned patent applications introduce aspherical surfaces for the purpose of reducing the overall glass thickness of the optical system and of improving transmittance. However, this has not lead to projection optical systems having large exposure regions and a sufficiently large numerical apertures.
The present invention relates to projection optical systems and exposure apparatus incorporating same and methods pertaining to same, and in particular to such systems, apparatus and methods for manufacturing devices and elements, such as integrated circuits, liquid crystal displays, CCD (charge coupled device) detectors, MR (magneto-resistive) heads, and the like.
The present invention takes the above problems into consideration and has several objectives.
The first objective to provide a compact high-performance projection optical system that is double-telecentric, and that includes an aperture stop capable of reducing the effects of vignetting when the numerical aperture (NA) is varied. A second objective is a projection optical system that is extremely well-corrected for the various aberrations, particularly distortion, while ensuring, through the use of aspherical lens surfaces, a sufficiently large numerical aperture and a large exposure field. A third objective to provide an exposure apparatus which includes with the abovementioned projection optical system, and a semiconductor device manufacturing method employing the exposure apparatus.
Accordingly, a first aspect of the present invention is a projection optical system capable of forming an image of an object. The system comprises, objectwise to imagewise, along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power and a first aspherical surface, and a fifth lens group having positive refractive power and an aperture. The projection optical system is designed such that paraxial rays traveling parallel to the optical axis imagewise to objectwise intersect the optical axis at a location Q between the fourth lens group and the fifth lens group. Further, at least one of the fourth and fifth lens groups includes a second aspherical surface arranged between the first aspherical surface in the fourth lens group and the aperture stop. Also, the fifth lens group includes a third aspherical surface arranged imagewise of the aperture stop. In addition, the following condition is satisfied:
0.01 less than dQ/{Lxc3x97(1xe2x88x92NA)} less than 0.4xe2x80x83xe2x80x83(1)
wherein the image and the object are separated by a distance L, the location Q and the aperture stop are separated by a distance dQ, and NA is an imagewise numerical aperture of the projection optical system.
A second aspect of the present invention is a projection optical system as described above, wherein the aperture stop has a variable size and is located imagewise of the location Q such that vignetting is minimized when the variable size is changed.
A third aspect of the invention is a projection optical system as described above, which satisfies the following conditions:
0.05 less than f1/L less than 0.5xe2x80x83xe2x80x83(2)
xe2x80x830.02 less than xe2x88x92f2/L less than 0.2xe2x80x83xe2x80x83(3)
0.04 less than f3/L less than 0.4xe2x80x83xe2x80x83(4)
0.03 less than xe2x88x92f4/L less than 0.3xe2x80x83xe2x80x83(5)
0.04 less than f5/L less than 0.4xe2x80x83xe2x80x83(6)
wherein f1 through f5 are focal lengths of the first through fifth lens groups, respectively.
A fourth aspect of the present invention is an exposure apparatus for imaging a pattern present on a reticle onto a photosensitive workpiece. The apparatus comprises a reticle stage for supporting the reticle, an illumination optical system adjacent the reticle stage for illuminating the reticle, a workpiece stage for supporting a workpiece, and the projection optical system as described above arranged between the reticle stage and the workpiece stage.
A fifth aspect of the present invention is a method of patterning a photosensitive workpiece with a pattern present on a reticle. The method comprises the steps of first illuminating the reticle, then projecting light from the reticle with the projection optical system as described above, and then exposing the photosensitive workpiece over an exposure field.
A sixth aspect of the present invention is a device manufacturing method comprising the steps of first coating a photosensitive material onto a substrate, then projecting onto the substrate the image of a pattern of reticle through the projection optical system as described above, then developing the photosensitive material on the substrate, thereby forming a photoresist pattern.